Probably either forgot or it wasn’t worth the trouble since they were on a short drive between locations.
It makes sense to wear a mask when you’re on an airplane or if you’re a service worker in constant contact with the general public.
Now for me personally wearing a mask was almost impossible to ignore because I wear glasses, so my glasses were constantly fogging up and it was a huge hassle and nearly unbearable over the course of a day, so in my mind it’s extra surprising to see people wearing masks when they’re alone and in my mind it doesn’t make much logical sense to do so.